Major - P3 The modifications to command_let_variables.js from related ticket SERVER-75356 added some test cases which run explain. But explain against a sharded cluster doesn't currently accept readConcern, so the test fails in the sharded_retryable_writes_downgrade passthrough with an error like this:
uncaught exception: Error: command failed: {
"ok" : 0,
"errmsg" : "Command explain does not support { readConcern: { level: \"majority\", afterClusterTime: Timestamp(1681916234, 13), provenance: \"clientSupplied\" } } :: caused by :: read concern not supported",
"code" : 72,
"codeName" : "InvalidOptions",